Plasma treatment system and cleaning method of the same

ABSTRACT

A plasma treatment apparatus has a reaction vessel ( 11 ) provided with a top electrode ( 13 ) and a bottom electrode ( 14 ), and the first electrode is supplied with a VHF band high frequency power from a VHF band high frequency power source ( 32 ), while the bottom electrode on which a substrate ( 12 ) is loaded and is moved by a vertical movement mechanism. The plasma treatment system has a controller ( 36 ) which, at the time of a cleaning process after forming a film on the substrate ( 12 ), controls a vertical movement mechanism to move the bottom electrode to narrow the gap between the top electrode and bottom electrode and form a narrow space and starts cleaning by a predetermined high density plasma in that narrow space. In the cleaning process, step cleaning is performed. Due to this, the efficiency of utilization of the cleaning gas is increased, the amount of exhaust gas is cut, and the cleaning speed is raised. Further, the amount of the process gas used is cut and the process cost is reduced.

TECHNICAL FIELD

The present invention relates to a plasma treatment system and acleaning method of the same, more particularly, relates to a large-sizedplasma treatment system and a method of cleaning the same which improvesthe efficiency of utilization of cleaning gas and reduces the amount ofPFC (perfluorocarbon) exhaust gas.

BACKGROUND ART

Conventional plasma CVD systems, for example, are mainly designed tosatisfy requirements in the deposition process. A cleaning process forcleaning the inside of the deposition chamber of the plasma CVD systemis merely performed as an added step of regulating the depositionprocess. Further, the deposition chamber is provided with a parallelplate type electrode comprised of a top electrode and a bottomelectrode. In the parallel plate type electrodes, high frequency poweris fed to the top electrode to generate discharge plasma in thedeposition chamber. As a frequency of the above high frequency power, afrequency of 13.56 MHz included in a HF band, which is designated inindustrial band specifications, is used. The bottom electrode functionsas a substrate holder. A substrate on which a film is deposited iscarried on it. Usually, the bottom electrode is attached by a fixedstructure. Further, the bottom electrode is usually made by an aluminumalloy or at least a part thereof is treated on it surface with alumiteor aluminum oxide. On the other hand, most of the top electrodes aremade by the same material as the bottom electrode. In some cases the topelectrode is made by pure aluminum.

As a document disclosing the prior art, Japanese Patent Publication (A)No. 10-237657 may be mentioned. The plasma treatment system disclosed inthis publication is comprised of a reaction vessel (10: referencenumeral used in the publication, same below) provided with a shower head(21) to which the high frequency power is supplied, and a susceptor (2)loading a substrate (70) and raised and lowered by a substrate elevationmechanism (50). The reaction vessel shows the structure in which theshower head (21) is fixed on the chamber (31) through an insulator (41).The insulator (41) electrically insulates the shower head (21) and thechamber (31).

In the development of the recent large-sized plasma CVD systems,priority is being given to the system concept of “raising the efficiencyof utilization of the PFC cleaning gas to cut the amount of exhaust”.According to this system concept, the system is being designed toincorporate requirements from the deposition process. Therefore, it isnot possible to position the cleaning process of the inside of thedeposition chamber as an additional process for the deposition processin the deposition chamber.

In the above plasma CVD system, using the frequency of 13.56 MHz has theadvantage of use of an industrial band, but production of high densityplasma by a system having the parallel plate type electrode isdifficult. This, in particular, has more important meaning in thecleaning process.

According to the conventional plasma CVD systems, the density of theplasma produced between the top electrode and the bottom electrode islow and bias voltage is not applied to the electrodes, so problems donot arise in the top electrode and bottom electrode produced by theabove materials. However, if making the density of the plasma higher orapplying a high bias voltage to the electrodes, several problems arisein the deposition process or cleaning process or in maintenance of thechamber.

When applying a high bias voltage for PFC plasma cleaning, for example,since the amount of fluorine radicals produced by dissociation of thePFC cleaning gas is large, the problem of corrosion occurs in the entiredeposition chamber with the conventional materials or structures.

When producing plasma of high density and depositing a film on thesubstrate by plasma CVD, the plasma is produced in the narrow spacebetween the top electrode and the bottom electrode. If the inner surfaceof the deposition chamber is exposed to the narrow space when usingplasma for CVD, film will easily deposit on the exposed inner surface.As a result, the problem arises that cleaning will become troublesomeand cleaning cannot be efficiently performed.

Further, in the conventional large-sized plasma CVD system, whenproducing plasma in a wide space for depositing film on the substrate byCVD, the film easily deposits on the entire inner surface of thedeposition chamber.

An object of the present invention is to provide a plasma treatmentsystem and a cleaning method of the same which eliminate the problem ofcorrosion and improve the efficiency of utilization of the cleaning gasso as to reduce the amount of exhaust gas and improve the cleaningefficiency.

Another object of the present invention is to provide a plasma treatmentsystem and a cleaning method of the same which reduce the filmdeposition on the inner surface of the chamber and improve the cleaningefficiency so as to reduce the amount of process gas used, improve theproductivity, and be of help in solving the problem of global warming.

DISCLOSURE OF THE INVENTION

The plasma treatment system and its cleaning method according to thepresent invention are configured as follows to achieve the above object.

The plasma treatment system according to the present invention iscomprised of a chamber able to be reduced to a vacuum, in which anelectrode structure including a first electrode and a second electrodeare provided. The first electrode is supplied with a high frequencypower from a VHF band high frequency power source. The second electrodehas a substrate stage and is moved up and down by a vertical movementmechanism. In the deposition process, the movement mechanism is used tomove the second electrode to narrow the gap between the first electrodeand the second electrode and form a narrow space. Predetermined plasmaof low density is generated in this narrow space. This plasma isutilized to deposit a film on a substrate. After the end of the filmdeposition or formation, the second electrode is made to move downwardand a substrate unloading mechanism is used to unload the substrate,then a cleaning process is performed. In the cleaning process, themovement mechanism is used to again move the second electrode to narrowthe gap between the first electrode and the second electrode and form anarrow space. Then, predetermined plasma of high density is used in thisnarrow space to start the cleaning process. A controller for executing acleaning operation controls the above cleaning process. In the usualconfiguration, the first electrode is the top electrode and the secondelectrode is the bottom electrode. The bottom electrode is typicallyraised and lowered in a state of loading the substrate.

In the above plasma treatment system, it is possible to generate highpower, high density plasma and start cleaning in a narrow space producedby the state of the first electrode and second electrode being made toapproach each other.

In the above plasma treatment system, preferably, the high density ofthe plasma is, as an indicator of electron density, at least 1E11 cm⁻³(10¹¹ cm⁻³), typically at least 5E11 cm⁻³ (5×10¹¹ cm⁻³).

In the above plasma treatment system, preferably, the inner wall of thechamber is covered by an insulator ring down to at least 2 cm (or 3 cm)from the main surface of the first electrode and the gap between theinsulator ring and sides of the second electrode is formed with aconstricted region having a gap of not more than 5 mm.

In the above plasma treatment system, preferably, the insulator ring ismade from alumite or aluminum oxide.

In the above plasma treatment system, preferably, an LF band lowfrequency from an LF band low frequency power source is superposed onthe high frequency power from the VHF band high frequency power source.

In the above plasma treatment system, preferably, the first electrodeand second electrode are both made from pure aluminum having an impurityconcentration of 1E-3 (10 ⁻³) or less.

The cleaning method of a plasma treatment system according to thepresent invention is a cleaning method for removing the films depositedon the inside surface of the chamber by plasma, after growing aninsulating film on a substrate by plasma CVD and then taking out thesubstrate out of the chamber. This cleaning process is comprised of afirst to third steps. In the first step, the gap between the firstelectrode and the second electrode is narrowed, a narrow space isformed, and cleaning is performed by the high density plasma created ina high power region of a VHF band high frequency. In the second step,the second electrode is lowered to the bottom surface of an insulatorring covering the inside wall of the chamber down from the main surfaceof the first electrode by a predetermined distance. In the third step,the second electrode is lowered to its lowest position and cleaning isperformed by the low density plasma produced in a low power region ofthe VHF band high frequency.

In the above cleaning method, preferably the narrow space formed betweenthe first electrode and the second electrode is at least a gap of 0.5cm, preferably a gap of 1 to 2 cm.

In the above cleaning method, preferably, the density of the highdensity plasma at the first step and the second step is at least 1E11cm⁻³, typically about 5E11 cm⁻³, while the density of the low densityplasma at the third step is about 1E10 cm⁻³.

In the above cleaning method, preferably, the high density plasma at thefirst step of the cleaning process is generated by superposing an LFband low frequency power from an LF band low frequency power source as abias voltage on the upper electrode etc. with respect to the highfrequency power from a VHF band high frequency power source. Further, atthe time of the second step as well, it is possible to superpose the LFband low frequency power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of the internal structure of aplasma treatment system according to an embodiment of the presentinvention;

FIG. 2 is a vertical sectional view of another state of the internalstructure of a plasma treatment system according to an embodiment of thepresent invention;

FIG. 3 is a view (A) partially showing the positional relationshipbetween an insulator ring and a deposition space and is a view (B) ofthe degree of film deposition in a Z-direction of a reaction vessel atthe time of film formation in a state where an insulator ring isprovided; and

FIG. 4 is a status diagram showing a simulation of the flow of gas atthe time of a deposition step.

BEST MODE FOR WORKING THE INVENTION

Below, a preferred embodiment of the present invention will be describedwith reference to the attached drawings.

The configurations, shapes, sizes, and positional relationshipsexplained in the embodiment are only shown schematically to the extentenabling understanding and working of the present invention. Further,the numerical values and compositions (materials) of the components areonly illustrations. Therefore, the present invention is not limited tothe following explained embodiment and can be modified in various waysso long as not exceeding the scope of the technical concept shown in theclaims.

In the following description, the explanation will be given taking as anexample a large plasma CVD system. However, the present invention is notlimited to this. It may also be generally applied to plasma treatmentsystems.

FIG. 1 and FIG. 2 are sectional views of the internal configuration of aplasma CVD system. This plasma CVD apparatus 31 has a parallel platetype electrode comprised of a top electrode 13 and a bottom electrode14. The top electrode 13 is supplied with two types of frequenciessuperposed from a high frequency power source 32 of the VHF band highfrequency and a low frequency power source 33 of a LF band lowfrequency. The bottom electrode 14 forms a substrate holder stage and isgrounded. The bottom electrode 14 has a substrate stage. The bottomelectrode 14 is provided with a vertical movement mechanism 35. Thisvertical movement mechanism (or elevator device) 35 raises and lowersthe bottom electrode 14. FIG. 1 shows the state where the bottomelectrode 14 is at its upper limit position, while FIG. 2 shows thestate where the bottom electrode 14 is at its lower limit position.

In the above description, the two facing electrodes were referred to asthe “top electrode” and “bottom electrode”, but they may also be a firstand a second electrode. The positions are not limited to top and bottomones.

The reaction vessel 11 forming a film deposition (or forming) chamber ismade by an air-tight structure and is set so that the inside becomes arequired vacuum state (reduced pressure state). The reaction vessel 11is made from a metal material and has conductivity. The reaction vessel11 is provided in practice with a port for loading and unloading thesubstrates to be treated or processed, an evacuation (or exhaust) portand evacuating device etc. for evacuating the inside to a requiredvacuum state, and a gas introduction mechanism for introducing adischarge gas for causing discharge. In FIG. 1 and FIG. 2, knownstructures are used for the above components, so for convenience inexplanation, their illustrations will be omitted.

The reaction vessel 11 is comprised of a cylindrical side member 41, aceiling member 42, and a floor member 43. The reaction vessel 11 isgrounded and is held at a ground potential. The floor member 43 issupported by a plurality of support columns 44 supporting the reactionvessel 11 as a whole. The center of the ceiling member 42 is formed withan opening. This opening has attached to it the top electrode 13 bybolts 46 through a ring-shaped insulator 45. The top electrode 13 iscomprised of a top member 13 a and a bottom member 13 b. A connectionterminal 47 provided at the center of the top surface of the top member13 a has a high frequency transmission cable 17 connected to it. Thebottom surface of the top member 13 a has the bottom member 13 b fixedto it by screws 48. The screws 48 simultaneously attach the ring-shapedinsulator 49 to the bottom edges of the bottom member 13 b of the topelectrode 13. The space between the top member 13 a and the bottommember 13 b and the inside of the top member 13 a are formed with a gaschannel 50 for carrying the process gas. Illustration of the gasintroduction mechanism for introducing a discharge gas into this gaschannel 50 is omitted.

The top electrode 13 and the bottom electrode 14 basically have the formof circular conductive plates overall and are arranged facing each otherin parallel across a desired gap. The gap between the top electrode 13and the bottom electrode 14 can be freely changed by changing the heightposition of the bottom electrode 14 by the vertical movement mechanism35.

The top electrode 13 is connected to the high frequency power source 32and the low frequency power source 33 through a matching circuit 34. Thehigh frequency power source 32 is a power source for outputting power ofa high frequency belonging to the VHF band for example, while the lowfrequency power source 33 is a power source for outputting power of alow frequency belonging to the LF band (or MF band) for example. Thehigh frequency of the power output from the high frequency power source32 is preferably 60 MHz, while the low frequency of the power outputfrom the low frequency power source 33 is preferably 400 kHz. Thefrequencies output from the power sources 32 and 33 are superposed bythe matching circuit 34 and supplied to the top electrode 13 in thesuperposed state. The high frequency and low frequency powers outputfrom the power sources 32 and 33 are supplied to the top electrode 13through the cable 17 and the connection terminal 47. The frequencysupplied to the top electrode 13 becomes energy of main discharge causedin the gap between the top electrode 13 and the bottom electrode 14.

The high frequency power source 32 is a power source for causing plasmadischarge and supplies the high power for producing high density plasma.The density is at least 1E11 cm⁻³, typically 5E11 cm⁻³ or more. Further,the lower frequency power source 33 is for giving a bias voltage fordetermining the collision energy of plasma ions. Note that the lowfrequency power supplied from the low frequency power source 33 can begiven selectively.

The substrate 12 is loaded on the top surface of the bottom electrode14. As shown in FIG. 2, when the bottom electrode 14 descends andreaches its lower limit position, the substrate 12 is supported by pushrods 51 and is in a state floating from the stage of the bottomelectrode 13. Further, as shown in FIG. 1, when the bottom electrode 14is at its upper limit position, since the bottom electrode 14 rises andmoves upward, the substrate 12 is carried in a state in contact with thetop surface of the bottom electrode 13.

When the bottom electrode 14 rises and is at its upper limit position,the space created by the top electrode 13 and the bottom electrode 14 isrelatively narrow, and thus a narrow space is formed. At this time, thegap (narrow space) between the bottom surface (main surface) of the topelectrode 13 and the top surface of the bottom electrode 13 ispreferably at least 0.5 cm, typically about 1 to 2 cm.

At the back surface side of the bottom electrode 14, a ring-shaped firstinsulator 52, a donut-shaped second insulator 53, a ring-shaped thirdinsulator 54 and a cylindrical fourth insulator 55 are arranged. Theback surface of the bottom electrode 14 and the surface of the supportcolumn 19 are all covered by the first to fourth insulators 52 to 55.Further, the surfaces of the second to fourth insulators 53 to 55 arecovered by the two conductive members 56, 57. The insulators 52 to 55are covered by the conductive members 56, 57 at all surfaces exposedinside the reaction vessel 11 except for the side surrounding surfacesof the first and second insulators 52, 53.

In the above configuration, an insulator ring 58 is provided so as tocover the inside wall of the reaction vessel 11 over a distance oftypically at least 2 cm (or 3 cm) down from the bottom surface of thefixed top electrode 13. This insulator ring 58 is made by a materialsuch as aluminum oxide strong against fluorine radicals (F radicals).Further, when the bottom electrode 14 is at the upper limit position,the distance between the surrounding side surfaces of the bottomelectrode 14 and the inner surface of the insulator ring 58 ispreferably not more than 5 mm. A constriction or constricted region 71is formed between the surrounding side wall of the bottom electrode 13and the inner surface of the insulator ring 58.

The support column 19 of the bottom electrode 14 has a rod shape. Thesupport column 19 is made from a material having conductivity. Thebottom end of the support column 19 is provided with a conductive flange61. The support column 19 of the bottom electrode 14 and the partsrelated to it extend to a region below the reaction vessel 11 through anopening 43 a formed in the floor member 43. These parts are surroundedby a bellows 21 attached to the bottom surface of the floor member 43 soas to cover the outside of the opening 43 a formed in the floor member43. The bellows 21 connects the edge of the opening 43 a and theperiphery of the flange 61 while maintaining an air-tight state.

As explained above, the reaction vessel 11 is grounded and maintained atthe ground potential. The bottom electrode 14 is electrically connectedto the reaction vessel 11 through the support column 19, the flange 61,and the bellows 21, so is similarly maintained at the ground potential.

In FIG. 1 and FIG. 2, the flange 61 is attached to the vertical movementmechanism 35. The flange 61 can be made to move up and down as shown bythe arrows 63 along the guide 62 by the vertical movement mechanism 35.Along with the vertical movement of the flange 61, the bottom electrode14 and the structural parts relating to the same also move up and down.The bellows 21 can structurally expand and contract, so expands andcontracts in a state maintaining the above air-tightness. Based on thisstructure, the bottom electrode 14 can be made to move up and down. Dueto this, it is possible to change the height position of the substrate12, change the gap (distance) between the top electrode 13 and thebottom electrode 14, and change the size of the gap. When causing maindischarge between the top electrode 13 and the bottom electrode 14 toproduce plasma and depositing a film based on the CVD action on thesubstrate 12 loaded on the bottom electrode 14, the bottom electrode 14is made to move to its upper limit position to reduce the distancebetween the top electrode 13 and the bottom electrode 14. In thestructure according to this embodiment, discharge is caused and plasmagenerated in a relative narrow gap space to form a film by CVD. When thefilm finishes being formed on the substrate 12, the vertical movementmechanism 35 makes the bottom electrode 14 move downward to widen thegap between the top electrode 13 and the bottom electrode 14. Due tothis, it becomes possible to change to a substrate 12 to be treatednext.

As explained above, due to the vertical movement mechanism 35, as shownin FIG. 1 and FIG. 2, the bottom electrode 14 and the structural partsrelating to it are raised and lowered between the lower limit positionand the upper limit position. The operation of the vertical movementmechanism 35 is controlled by the controller 36 comprised by a computer.The memory provided in the controller 36 stores various programs forexecuting the deposition process and the cleaning process.

Note that a conductive cover 60 is fixed to the top side of the reactionvessel 11. The cover 60 shields the insides from high frequencies. Thecover 60 protects the top side of the top electrode 13 in the reactionvessel 11 from high frequencies.

In the structure shown in FIG. 1 and FIG. 2, the structural portion ofthe back surface of the bottom electrode 14 is covered by the insulators52 to 56 at all of the outer surface of the connecting portion (supportcolumn 19) up to the ground potential portion (flange portion) includingthe back surface of the bottom electrode 14. As a result, it is possibleto prevent the undesirable generation of discharge at the back surfaceside of the bottom electrode 14.

In the above plasma CVD system, usually when the bottom electrode 14rises to the upper limit position, the position of the bottom electrode14 is the position where the film deposition process is performed. Whenthe bottom electrode 14 descends, the position of the bottom electrode14 is the position for transport of the substrate. Further, at the timewhen the film deposition process ends, plasma is created for cleaning ata suitable timing (after unloading substrate etc.) This cleaning processis a step cleaning comprised of a plurality of steps. In this stepcleaning, at the first step, the bottom electrode 14 is moved to theupper limit position and plasma discharge is caused in the narrow spaceto generate the high density plasma for cleaning. At the final step ofthe step cleaning, the bottom electrode 14 is made to descend to thelower limit position. At the final step of cleaning, the low densityplasma is used.

In the reaction vessel 11 of a large-sized plasma CVD system shown inFIG. 1 and FIG. 2, the electrode gap between the top electrode 13 andthe bottom electrode 14 at the time of the deposition process is 1 to 2cm, more preferably 1 cm, that is, the narrow gap or narrow space systemis employed. That is, the system is configured for so-called narrowspace film deposition. By making the electrode gap narrow in this way,sealing the plasma between the electrodes becomes easy.

Further, the bottom electrode 14 on which the substrate 12 is loaded isgrounded through a structure bypassing the high frequency power. Thisstructure, as explained above, is based on a coaxial structure comprisedof a first metal part (support column 19), insulator part (fourthinsulator 55) and second metal part (conductive member 57). The supportcolumn 19 and the conductive member 57 are electrically connected by theterminal flange 61 and grounded. By this structure, the feedback highfrequency will not leak from the bottom electrode 14. Therefore,discharge will not occur below the bottom electrode 14. This isconfirmed from electromagnetic field simulations as well.

By adopting the structure explained above, it is possible to seal theplasma in the space between the electrodes, and plasma is not producedat the space below the bottom electrode stage. Therefore, it becomespossible to prevent film deposition at parts of the space below thebottom electrode stage.

Further, since the insulator ring 58 is provided as explained above, inthe film deposition process, it is possible to reduce the filmdeposition on the exposed inner surface of the reaction vessel 11. Thereasons will be explained in detail next.

FIG. 3 is a view explaining the above reasons. In FIG. 3, (A) partiallyshows the positional relationship between the insulator ring 58 and thedeposition space 81 formed as a narrow space, while (B) shows the extentof film deposition in the Z-direction of the reaction vessel 11 at thetime of film formation in the state where the insulator ring 58 isprovided. In (A) of FIG. 3, the Z-direction is shown, while in (B) ofFIG. 3, the abscissa shows the distance (unit of cm) in the Z-directionand the ordinate shows the thickness (unit of angstroms (Å)) of the filmdeposited on the inner wall surface of the reaction vessel 11. As shownin (A) of FIG. 3, if performing the film deposition process when thedistance D between the top electrode 13 and the bottom electrode 14 is 2cm for example, and the film forming space is a narrow space, as clearfrom (B) of FIG. 3, at the inner wall surface of the reaction vessel 11,film deposits to a thickness of about 10⁴ Å until about 2 cm below thebottom surface of the top electrode 14, the amount of deposition of filmis greatly reduced between 2 cm to 3 cm, and the thickness becomes about10 Å about 3 cm from the bottom surface of the top electrode. Therefore,if considering the cleaning process of the inner surface of the reactionvessel 11 after this, it is preferable to use an insulator ring 58 tocover down to a location about 3 cm from the bottom of the top electrode14.

Next, the cleaning process will be explained. In the cleaning of theinside of the reaction vessel 11, the step cleaning is performed. Thestep cleaning is a cleaning process expanding the plasma space step bystep along with the elapse of time. It is a cleaning method comprised ofa plurality of steps with different conditions. In the step cleaning, atthe start of the cleaning, the bottom electrode 14 rises to the positionfor the film deposition process and the plasma space is made narrow.Therefore, in the cleaning in this state, it is possible to focus thehigh frequency power at the two electrodes of the top electrode 13 andthe bottom electrode 14 where the film is deposited the thickest. Next,by lowering the bottom electrode 14 in stages or in steps, the wallsurface is cleaned in a wider space formed by the top electrode 13, thebottom electrode 14, and part of the reaction vessel 11. At the finalstage of the step cleaning, the bottom electrode 14 descends to theposition carrying the substrate, whereby the heads of the lift pinssticking out from the surface of the stage of the bottom electrode 14 onwhich the substrate 12 is loaded are cleaned.

More specifically, the cleaning process is preferably comprised of afirst to third steps.

In the first step, the gap between the top electrode 13 and the bottomelectrode 14 is made a narrow space and cleaning is performed by thehigh density plasma generated by a high power region of the VHF bandhigh frequency. At this time, a bias voltage is applied to the topelectrode 13 by the lower frequency power source 33 simultaneously.

In the second step, the bottom electrode 14 is made to descend from thebottom surface (main surface) of the top electrode 13 to the bottomsurface of the insulator ring 58 and in that state cleaning is performedusing the high density plasma formed in the high power region of the VHFband high frequency. In this second step, preferably, a bias voltage isnot supplied from the low frequency power source 33. Cleaning is onlyperformed under conditions of the high density plasma. Note that it isalso possible to apply the above bias voltage.

In the third step, the bottom electrode 14 is made to descend to thelowest position and cleaning is performed using the low density plasmaformed in the low power region of the VHF band high frequency.

Note that when utilizing a VHF band high frequency power to generateplasma, it is possible to adjust the power in order to adjust thedensity of the plasma.

In the first step and the second step, the insulator ring 58 covers theinside surface of the reaction vessel 11, so it is possible to utilizehigh density plasma for cleaning. In the third step, the inner surfaceof the reaction vessel 11 appears and the reaction vessel 11 is made byan aluminum alloy, so low density plasma is used for cleaning.

The density of the high density plasma in the first step and second stepin the above cleaning method is at least 1E11 cm⁻³, preferably about5E11 cm⁻³, while the density of the lower density plasma in the thirdstep is about 1E10 cm⁻³.

Note that in the above step cleaning, the number of steps and at whichtiming to perform the steps can be freely determined in accordance withthe objective and in accordance with the system.

In the present embodiment, the high density plasma is produced by theVHF band high frequency (typically 60 MHz) power supplied from the highfrequency power source 32. It is known that by raising the excitationfrequency of the plasma, it is possible to raise the plasma density, butin the present embodiment, the plasma density is raised to promote thehigher order dissociation of the cleaning gas. As a result, it ispossible to increase the amount of F radicals effective for etching theoxide film and possible to reduce the production of the high globalwarming coefficient byproduct CF₄ etc. (ancillary production).

The reaction vessel 11 of the large-sized plasma CVD system according tothe present embodiment, is provided with a high frequency power source32 for supplying a plasma excitation high frequency of 60 MHz and 3 kWfor example, instead of the conventional 13.56 MHz. Further, a lowfrequency power source 33 for biasing processing at 400 kHz is built infor the purpose of improving the etching rate of the oxide film by ioncollision. That is, in the present embodiment, to stably transmit a highfrequency, a low frequency of 400 kHz is superposed on the highfrequency to be applied to the top electrode 13.

Further, in the above plasma CVD system, since the film is depositedusing the space between the top electrode 13 and the bottom electrode 14as a narrow space, it is possible to secure uniformity of filmdeposition. To secure uniformity of film deposition in the narrow space,improvement of the precision of the parts is sought. In general, thepoints when making film deposition uniform on the surface of a substrate12 are to generate uniform plasma and to create a distribution ofdensity of gas with a good uniformity above the bottom electrode 14.From this viewpoint, the plasma CVD system of the present embodiment hasthe following characteristics.

A distribution of gas density with a good uniformity is formed on thestage of the bottom electrode 14. This plasma CVD system also suppliesgas through a shower head provided at the top electrode 13. The firstfactor determining the uniformity of the distribution of the gas densityabove the bottom electrode 14 is the array of shower holes in the showerhead. To enable the uniform supply of gas molecules even with anelectrode gap of 1 cm, the distance between shower holes is preferablymade 4 mm.

The second factor determining the uniformity of the distribution of thegas density is that the flow of gas is created symmetrically anduniformly above the bottom electrode 14. Therefore, a constriction ornarrow path 71 is provided between the sides of the bottom electrode 14and the insulator ring 58 provided at the inside wall of the reactionvessel 11, whose distance is 5 mm. The conductance of the flow of gas atthe constriction 71 becomes smaller. Therefore, the flow of gas at thespace between the top electrode 13 and the bottom electrode 14 becomesresistant to the effects of the distribution of conductance below thereaction vessel 11. As a result, despite the side gas evacuation usingthe evacuation port at the wall of the reaction vessel below the bottomelectrode 14, it is possible to obtain a flow of gas with good symmetryin the space between the electrodes.

The flow of the gas in the film deposition process will be explainednext. The state of simulation of the flow of gas for only the case wherethe electrode gap at the time of the film deposition process is 1 cm isshown in FIG. 4 based on the above perspective. First, the results inthe case of use of Ar gas as the gas are shown. The results ofsimulation when fixing the pressure at the evacuation port at 300 Pa andchanging the flow rate of the gas introduced from the shower part of thetop electrode 13 to 500 sccm are shown. As clear from the simulation, asexplained above, by making the gap or distance of the constriction 71preferably 5 mm, a flow of gas 91 with no swirls etc. is obtained. FIG.4 is shown simplified, but in actuality a smooth flow of gas 91comprised of a plurality of layers is created.

In the above description, both the top electrode 13 and the bottomelectrode 14 were made from pure aluminum with an impurity concentrationof not more than 1E-3, so corrosion by F radicals becomes small.

Further, at the above first step, the LF band high frequency power fromthe low frequency power source 33 is utilized to apply an electric field(bias) at the surfaces of the top electrode 13, the bottom electrode 14,and the insulator, but if the electric field is made stronger, it ispossible to increase the cleaning rate by the effect of the ion kineticenergy.

Note that as specific examples, when depositing a silicon oxide filmonto the substrate, SiH₄, N₂O, or diluted Ar is used as the process gasand conditions of a pressure of 300 Pa and a substrate temperature of300° C. are set. Further, when depositing a silicon nitride film ontothe substrate, SiH₄, NH₃, or N₂ is used as the process gas andconditions of a pressure of 300 Pa and a substrate temperature of 300°C. are set. Further, as the cleaning process, C₂F₆ (perfluorocarbon) orO₂ is set and the cleaning rate is increased by the above step cleaning.

According to the present invention, since the step cleaning is adoptedin the cleaning process in a large-sized plasma CVD system, for example,it is possible to enhance the efficiency of utilization of the cleaninggas, possible to cut the amount of exhaust gas by this, possible toraise the cleaning rate, possible to improve the productivity, possibleto cut the amount of process gas used, and possible to reduce the costs.In particular, since it is possible to improve the dissociation of C₂F₆by the high density plasma cleaning in the first step and second step,it is possible to cut the amount of use and possible to reduce theproduction of the high global warming coefficient byproduct CF₄ etc., soit is possible to help solve the problem of global warming. Further,since the film deposition chamber is covered by an insulator ring downto a predetermined distance from the main surface of the top electrode,it is possible to reduce the amount of film deposition on the innersurface of the deposition chamber.

INDUSTRIAL APPLICABILITY

The plasma treatment system and cleaning method of the same according tothe present invention raise the efficiency of utilization of thecleaning gas, cut the amount of exhaust gas, and raise the cleaningrate. Further, they cut the amount of process gas used, reduce theprocess cost, and are helpful in solving the problem of global warming.

1. A cleaning method of a plasma treatment system, for growing aninsulating film on a substrate by plasma CVD, then taking out thesubstrate, and then removing the film deposited inside a chamber byplasma, wherein the plasma treatment system is constructed to cover aninside wall of the chamber down to at least 3 cm from a main surface ofa first electrode by an insulator ring, the cleaning method comprisingsequential steps of: forming a gap between the first electrode and asecond electrode of at least 0.5 cm and a gap of not more than 5 mmbetween the insulator ring and the second electrode, and performing afirst cleaning by generating a first density plasma, lowering the secondelectrode to a bottom surface of the insulator ring, and performing asecond cleaning by generating the first density plasma, and lowering thesecond electrode to its lowest position lower than the bottom surface ofthe insulator ring, and performing a third cleaning by generating asecond density plasma having a density lower than the first densityplasma, the first density plasma and second density plasma beinggenerated by power of a very high frequency.
 2. A cleaning method of aplasma treatment system as set forth in claim 1, wherein the gap formedbetween the first electrode and the second electrode is 1 to 2 cm.
 3. Acleaning method of a plasma treatment system as set forth in claim 1,wherein the density of the first density plasma is substantially 5×10¹¹cm⁻³ and the density of the second density plasma is substantially1×10¹⁰ cm⁻³.
 4. A cleaning method of a plasma treatment system as setforth in claim 1, wherein the first density plasma of the first cleaningis generated by superposing a power of a low frequency or mediumfrequency on the supplied very high frequency power.
 5. A cleaningmethod of a plasma treatment system as set forth in claim 1, wherein thefirst density plasma of the first cleaning and second cleaning isgenerated by superposing a power of a low frequency or medium frequencyon the supplied very high frequency power.